1. Field of the Invention
The present invention relates to filter assemblies of the mechanical, electronic and electrostatic nature. More particularly, the invention relates to a water repellent barrier for use with mechanical, electronic and electrostatic filter assemblies to prevent water droplets from entering the filter assembly and lessening the effectiveness of, or destroying, the filter media.
Most particularly, the present invention relates to a hydrophobic barrier placed in sealing engagement with the upstream or intake and/or downstream or exhaust side of a filter assembly.
2. Description of the Prior Art
Generally, filter assemblies fall into one of three categories. Mechanical filters, electronic filters, and electrostatic (non-powered electronic) air filters. A mechanical filter generally consists of a flat, or pleated, mat of fibers (the "filter media") contained in a supporting frame. This type of filter removes particles from the air passing through it by collecting them as they impact on individual fibers, or are too large to pass between fibers. The percentage of particulates trapped determines the filter's overall efficiency, e.g. four percent, twenty percent, fifty percent, or eight-five percent, etc. The typical "furnace filter" will be of a low resistance with very low efficiency. A "high tech filter", the HEPA (High Efficiency Particle Arrestor) filter will be a high resistance filter with a high particulate removal efficiency.
The second category of filter assemblies is that of the powered electronic air cleaner. Powered electronic air cleaners draw air in through a front section which electrically charges the incoming particles with a positive charge, and then passes these particles between a series of plates which are alternately positive and ground. Positive particles in the air stream are repelled away from the positive plates over to the grounded plates where they collect. Because of their very open configuration, such units naturally have a very low resistance to air flow.
The third category of filter apparatus is the non-powered electronic or electrostatic air filter. Electrostatic air filters have either an electret media or a triboelectric media.
An electret media is a filter media having plastic fibers which are permanently charged by heating and cooling them in an electric field during manufacture. The fibers then contain both positive and negative charges on the surface.
A triboelectric filter media contains at least two different types of polymer fibers and are charged by the rubbing of the fibers during manufacture or use. One fiber becomes positively charged, and the other becomes negatively charged. A good discussion of the different types of air filters and examples thereof is contained in U.S. Pat. No. 5,549,735 issued Aug. 27, 1997 to Rex R. Coppom. The specification of the Coppom patent is specifically incorporated herein by reference.
Those skilled in the art are coming to realize that all three of these types of filter assemblies or units can suffer a loss of efficiency, or other problems, if the media therein is contaminated by water droplets. Water droplets, as opposed to water vapor, can saturate or discharge the media depending on the type of filter, and result in a loss in efficiency.
The problems caused in mechanical type filters by being impacted by water droplets, such as might occur in a home heating system installed in a home having an "ultrasonic" humidifier discharging fine water droplets into the air, have been found to be of three types. First, if the media is not hydrophobic, the fibers in the media may swell, and cause an increased flow resistance.
Second, the impact of water droplets may "wash off" previously captured particles if the size thereof is smaller than the pore structure of the filter. Third, if a mechanical filter with a tight pore structure is involved, the filter can plug up.
In an electronic filter, a different type of problem exists. The problem of "popping" when wet with regard to electronic filters is discussed in the U.S. Pat. No. 5,232,478 issued Aug. 3, 1993 to Richard W. Farris. The specification of the Farris patent is herein specifically incorporated by reference. As described in said patent, cleaning conventional permanent electronic air filters involves saturating a collecting cell in water. If the air filter is reinstalled in the furnace and energized before the collecting cell has completely dried, high voltage arcing will occur through the filter media between the high voltage grid and the grounded grills. While such arcing is not necessarily damaging, it creates a loud and annoying "popping" sound which can continue for an appreciable length of time.
It is believed that the continuation of such "popping" for a considerable length of time may be due to water droplets circulating in the heating system and/or water droplets entering the heating system from ultrasonic humidifiers. Also, even when dry, it is believed that water droplets entering the heating system from ultrasonic humidifiers will occasionally cause this annoying "popping" sound.
While the solution presented in said U.S. Pat. No. 5,232,478 is generally satisfactory for preventing the "popping" after a complete immersion of the filter in water, during the time the filter is wet, it is grounded, and has no cleaning efficiency. Thus, it is not an entirely satisfactory solution. Further it provides no answer as to how to prevent water droplets from circulating in the heating system, either from the air cleaner itself, or from ultrasonic humidifiers. Therefore, those skilled in the art of electronic filters have continued to search for a satisfactory solution for removing water droplets from a heating system in which it is installed.
Electrostatic filters, used widely in the medical and other areas, depend on the positive and negative charges appearing on the fibers to attract oppositely charged particles. It is believed that water droplets trapped by an electret, or triboelectric media, or any other media that can be charged, or that depends on charging as the main mechanism for particle removal, will short out or neutralize the media in the areas where the water droplets lodge, resulting in a great decrease in efficiency as long as the water droplets are present in the filter. Thus, it would be very desirable to have a barrier to remove these water droplets.